U.S. patent application number 11/346890 was filed with the patent office on 2006-08-24 for method of manufacturing semiconductor device and semiconductor device.
Invention is credited to Yoshiyuki Enomoto, Hiroyuki Kawashima, Masaki Okamoto.
Application Number | 20060186548 11/346890 |
Document ID | / |
Family ID | 36911823 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060186548 |
Kind Code |
A1 |
Enomoto; Yoshiyuki ; et
al. |
August 24, 2006 |
Method of manufacturing semiconductor device and semiconductor
device
Abstract
The present invention provides a method of manufacturing a
semiconductor device and a semiconductor device that allow use of
interlayer and interconnect insulating films having a low
dielectric constant in forming a dual damascene structure. A first
insulating film, a second insulating film, a first-mask forming
layer, a second-mask forming layer, a third-mask forming layer, and
a fourth-mask forming layer are sequentially deposited over a
substrate. The fourth-mask forming layer is patterned to form a
fourth mask having an interconnect trench pattern. After a resist
mask is formed on the fourth mask, the layers to the second
insulating film are etched to open via holes. The third-mask
forming layer is etched through the fourth mask to thereby form a
third mask having the interconnect trench pattern and to extend the
via holes downward partway across the first insulating film. The
second-mask forming layer is etched through the fourth mask to
thereby form a second mask having the interconnect trench pattern,
and the first insulating film that remains under the bottoms of the
via holes is removed. Subsequently, the second insulating film is
etched through the second mask to thereby form an interconnect
trench, and then the second mask is removed.
Inventors: |
Enomoto; Yoshiyuki;
(Kanagawa, JP) ; Kawashima; Hiroyuki; (Kanagawa,
JP) ; Okamoto; Masaki; (Kanagawa, JP) |
Correspondence
Address: |
ROBERT J. DEPKE;LEWIS T. STEADMAN
ROCKEY, DEPKE, LYONS AND KITZINGER, LLC
SUITE 5450 SEARS TOWER
CHICAGO
IL
60606-6306
US
|
Family ID: |
36911823 |
Appl. No.: |
11/346890 |
Filed: |
February 3, 2006 |
Current U.S.
Class: |
257/758 ;
257/E21.582; 257/E23.145; 257/E23.167 |
Current CPC
Class: |
H01L 21/76829 20130101;
H01L 2924/00 20130101; H01L 21/76811 20130101; H01L 21/76838
20130101; H01L 23/5226 20130101; H01L 21/76835 20130101; H01L
21/76832 20130101; H01L 2924/0002 20130101; H01L 21/76813 20130101;
H01L 23/5329 20130101; H01L 21/76808 20130101; H01L 21/76814
20130101; H01L 23/53238 20130101; H01L 2924/0002 20130101; H01L
23/53295 20130101 |
Class at
Publication: |
257/758 |
International
Class: |
H01L 23/52 20060101
H01L023/52 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2005 |
JP |
2005-035414 |
Dec 15, 2005 |
JP |
2005-361211 |
Claims
1. A method of manufacturing a semiconductor device having an
insulating film that includes a low dielectric constant (low-k)
material film having a dielectric constant smaller than a
dielectric constant of silicon dioxide, the method comprising the
steps of: (a) sequentially forming a first insulating film and a
second insulating film over a substrate that includes a conductive
layer pattern in a region including a front surface of the
substrate, the first insulating film serving as an interlayer
insulating film between interconnect layers and being composed of a
low-k material, the second insulating film serving as an insulating
film among interconnects and being composed of a low-k material
different from the material of the first insulating film; (b)
sequentially forming a first-mask forming layer, a second-mask
forming layer, a third-mask forming layer, and a fourth-mask
forming layer over said second insulating film, the first-mask
forming layer being composed of a low-k material different from the
material of the second insulating film, the second-mask forming
layer being composed of an insulating material different from the
material of the first-mask forming layer, the third-mask forming
layer being composed of an insulating material different from the
material of the second-mask forming layer, the fourth-mask forming
layer being composed of an insulating material different from the
third-mask forming layer; (c) patterning said fourth-mask forming
layer to thereby form a fourth mask having an interconnect trench
pattern; (d) forming a resist mask having a via hole pattern on
said fourth mask and said third-mask forming layer; (e) with use of
said resist mask as an etching mask, etching said fourth mask, said
third-mask forming layer, said second-mask forming layer, and said
first-mask forming layer and etching said second insulating film,
to thereby open a via hole; (f) with use of said fourth mask as an
etching mask, etching said third-mask forming layer to thereby form
a third mask having the interconnect trench pattern, and etching
said first insulating film to an intermediate thickness of said
first insulating film to thereby extend said via hole downward; (g)
with use of said fourth mask and said third mask as an etching
mask, etching said second-mask forming layer to thereby form a
second mask having the interconnect trench pattern, and etching
said first insulating film that remains under the bottom of said
via hole to thereby extend said via hole downward so that said via
hole reaches said substrate, said fourth mask being removed as a
result of the etching of said second-mask forming layer; (h)
etching said first-mask forming layer with use of said third mask
as an etching mask, to thereby form a first mask having the
interconnect trench pattern; (i) after removal of said third mask,
forming an interconnect trench in said second insulating film with
use of said second mask as an etching mask; and (j) removing said
second mask after the forming of the interconnect trench.
2. The method of manufacturing the semiconductor device according
to claim 1, wherein: in said step (a), an etching stopper film that
prevents said substrate being etched in the etching of said steps
(g) and (h) is formed on said substrate, and said first insulating
film and said second insulating film are sequentially formed over
the etching stopper film; in said step (g), said via hole is
extended downward so that said via hole reaches said etching
stopper film; and in said step (i), said etching stopper film is
removed in addition to said third mask.
3. The method of manufacturing the semiconductor device according
to claim 2, wherein: said etching stopper film includes a first
etching stopper film and a second etching stopper film, the first
etching stopper film being provided on said substrate and
preventing diffusion of a conductive material from said conductive
layer pattern, the second etching stopper film being provide on the
first etching stopper film; and said second etching stopper film is
composed of a material that is less susceptible to being etched in
the etching of said step (h) than a material of said first etching
stopper film.
4. The method of manufacturing the semiconductor device according
to claim 3, wherein said second etching stopper film is composed of
silicon oxide having high silicon content.
5. The method of manufacturing the semiconductor device according
to claim 1, further comprising between said step (i) and said step
(j): forming a conductive film on said second mask in a manner of
filling the interconnect trench pattern of said second mask and
said first mask, said interconnect trench, and said via hole,
wherein in said step (j), extra part of said conductive film
unnecessary as an interconnect pattern is removed in addition to
said second mask by chemical mechanical polishing.
6. The method of manufacturing the semiconductor device according
to claim 1, wherein in said step (j), said second mask is removed
such that part of said second mask of a thin film shape remains on
the whole or part of said first mask.
7. A method of manufacturing a semiconductor device having an
insulating film that includes a low dielectric constant (low-k)
material film having a dielectric constant smaller than a
dielectric constant of silicon dioxide, the method comprising the
steps of: (a) sequentially forming a first insulating film and a
second insulating film over a substrate that includes a conductive
layer pattern in a region including a front surface of the
substrate, the first insulating film serving as an interlayer
insulating film between interconnect layers and being composed of a
low-k material, the second insulating film serving as an insulating
film among interconnects and being composed of a low-k material
different from the material of said first insulating film; (b)
sequentially forming a first-mask forming layer, a second-mask
forming layer, a third-mask forming layer, and a fourth-mask
forming layer over said second insulating film, the first-mask
forming layer being composed of a low-k material different from the
material of the second insulating film, the second-mask forming
layer being composed of an insulating material different from the
material of the first-mask forming layer, the third-mask forming
layer being composed of an insulating material different from the
material of the second-mask forming layer, the fourth-mask forming
layer being composed of an insulating material different from the
third-mask forming layer; (c) patterning said fourth-mask forming
layer, said third-mask forming layer, and said second-mask forming
layer to thereby form a via hole pattern in said fourth-mask
forming layer, said third-mask forming layer, and said second-mask
forming layer; (d) forming a resist mask having an interconnect
trench pattern over said fourth-mask forming layer having the via
hole pattern; (e) etching the fourth-mask forming layer with use of
said resist mask as an etching mask, to thereby form a fourth mask
having the interconnect trench pattern; (f) etching said first-mask
forming layer with using, as an etching mask, said third-mask
forming layer and said second-mask forming layer that have the via
hole pattern, to thereby form the via hole pattern in said
first-mask forming layer, and etching said third-mask forming layer
with using said fourth mask as an etching mask, to thereby form a
third mask having the interconnect trench pattern; (g) opening a
via hole in said second insulating film with use of said
second-mask forming layer having the via hole pattern as an etching
mask; (h) with use of said fourth mask and said third mask as an
etching mask, etching said second-mask forming layer to thereby
form a second mask having the interconnect trench pattern, and
extending said via hole downward partway across said first
insulating film, said fourth mask being removed as a result of the
etching; (i) with use of said third mask as an etching mask,
etching the first-mask forming layer to thereby form a first mask
having said interconnect trench pattern, and etching said first
insulating film that remains under the bottom of said via hole to
thereby extend said via hole downward so that said via hole reaches
said substrate; (j) after removal of said third mask, forming an
interconnect trench in said second insulating film with use of said
second mask as an etching mask; and (k) removing the second mask
after the forming of said interconnect trench.
8. The method of manufacturing the semiconductor device according
to claim 7, further comprising between said step (j) and said step
(k): forming a conductive film on said second mask in a manner of
filling the interconnect trench pattern of said second mask and
said first mask, said interconnect trench, and said via hole,
wherein in said step (k), extra part of said conductive film
unnecessary as an interconnect pattern is removed in addition to
said second mask by chemical mechanical polishing.
9. A semiconductor device having an insulating film that includes a
low dielectric constant (low-k) material film having a dielectric
constant smaller than a dielectric constant of silicon dioxide,
comprising: a first insulating film that is composed of a low-k
material and is provided over a substrate that includes a
conductive layer pattern in a region including a front surface of
the substrate; a second insulating film that is provided on the
first insulating film and is composed of a low-k material different
from the material of said first insulating film; a third insulating
film that is provided on the second insulating film and is composed
of a low-k material different from the material of said second
insulating film; a via that is provided in said first insulating
film and reaches said substrate; an interconnect that is provided
in said second insulating film and said third insulating film, and
reaches said via; and a thin-film fourth insulating film that is
provided on the whole or part of said third insulating film, and is
composed of an insulating material different from the material of
said third insulating film.
10. The semiconductor device according to claim 9, further
comprising: an etching stopper film that is provided between said
substrate and said first insulating film, and prevents said
substrate from being etched in etching of said first insulating
film.
11. The semiconductor device according to claim 10, wherein: said
etching stopper film includes a first etching stopper film and a
second etching stopper film, the first etching stopper film being
provided on said substrate and preventing diffusion of a conductive
material from said conductive layer pattern, the second etching
stopper film being provide on said first etching stopper film; and
said second etching stopper film is composed of silicon oxide
having high silicon content.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present invention contains subject matter related to
Japanese Patent Application JP 2005-035414 filed with the Japanese
Patent Office on Feb. 14, 2005 and Japanese Patent Application JP
2005-361211 filed with the Japanese Patent Office on Dec. 15, 2005,
the entire contents of which being incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a method of manufacturing a
semiconductor device and a semiconductor device, and particularly
to a method of manufacturing a semiconductor device having a
multilevel interconnect structure based on a dual damascene
structure that has a structural shape suitable for adoption of low
dielectric constant (low-k) films as interlayer insulating films
and insulating films among interconnects (interconnect insulating
films), and the semiconductor device.
[0003] In step with size miniaturization and increase of
integration degree of semiconductor devices, delays of electrical
signals attributed to the time constant of interconnects are
increasingly becoming a serious problem. Accordingly, for
conductive layers in a multilevel interconnect structure, use of
copper (Cu) interconnects, which have a low resistivity, has been
advanced instead of aluminum (Al) alloy interconnects. The Cu,
however, is difficult to pattern by dry etching unlike metal
materials such as Al used in conventional multilevel interconnect
structures. Therefore, typically multilevel Cu interconnect
structures employ a damascene method, in which interconnect
trenches are formed in insulating films, and then Cu films are
buried in the interconnect trenches. In particular, a dual
damascene method is attracting attention. In this method, after
formation of via holes and interconnect trenches, Cu is buried in
the holes and trenches simultaneously. The dual damascene method
therefore is advantageous for reducing the number of steps. For
example, Japanese Patent Laid-open No. Hei 11-45887 discloses this
method.
[0004] In addition, in high-integration semiconductor devices, an
increase of interconnect capacitance causes lowering of operation
speed of the semiconductor devices. Therefore, It is essential to
the semiconductor devices to employ minute multilevel interconnects
for which low-k materials are used as interlayer and interconnect
insulating films to suppress the increase of interconnect
capacitance. Currently used as the low-k materials are substances
having a dielectric constant of about 2.7, such as organic polymers
typified by polyarylether (PAE) and inorganic materials typified by
hydrogen silsesquioxane (HSQ) and methyl silsesquioxane (MSQ). In
addition to these materials, in recent years, adoption of low-k
materials having a dielectric constant of about 2.2 obtained by
making the above-described materials porous is being promoted.
[0005] When the dual damascene method is applied to interlayer and
interconnect insulating films including low-k material films, it is
required to address the following technical restrictions.
[0006] The first restriction is that the compositions of the low-k
material films are close to the composition of resist used for
patterning, and therefore the low-k material films are readily
damaged in a resist removal process. Specifically, it is essential
that damage to the low-k material films can be suppressed in resist
removal treatment after etching with use of a resist mask, and in
resist reproduction treatment when a treated resist mask does not
satisfy the product standard.
[0007] The second restriction is that the manufacturing process
needs to have applicability to fabrication of a borderless
structure, in which there is no alignment margin between
interconnects and via holes. In step with miniaturization of
semiconductor devices, employment of a manufacturing process
compatible with a borderless structure becomes a major premise of
achievement of multilevel interconnects after the 0.18 .mu.m
generation. Therefore, also in simultaneous formation, in a dual
damascene method, of interconnect trenches and via holes in
interlayer and interconnect insulating films including low-k
materials, it is important to employ a process involving less
variation in the via resistance due to misalignment.
[0008] The third restriction is that adoption of a layer with a
comparatively high dielectric constant leads to an increase of
interconnect capacitance. Specifically, in order to form
interconnect trenches with adequately controlling the depth
thereof, it is desirable to provide, near the bottoms of the
interconnect trenches, a layer that has a large etching selection
ratio with respect to interlayer and interconnect insulating films.
However, when a layer with a comparatively high dielectric constant
is used for that purpose, an increase of interconnect capacitance
is caused. Therefore, there has been a need for a dual damascene
process for an interlayer and interconnect insulating structure
employing low-k materials, allowing control of formation of
interconnect trenches combined with suppression of a capacitance
increase.
[0009] As a dual damascene method that can address the
above-described technical restrictions, a method has been proposed
that will be described below with reference to FIGS. 7A to 7H,
which are sectional views of manufacturing steps. For example,
Japanese Patent Laid-open No. 2004-63859 discloses this method.
[0010] Referring initially to FIG. 7A, on a base insulating film 2
deposited on a silicon substrate 1, a multilayer film formed of a
polyarylether (PAE) film 3 and a silicon dioxide film (SiO.sub.2) 4
are deposited as an interconnect insulating film. Subsequently,
buried interconnects (Cu interconnects) 7 formed of a copper (Cu)
film are formed in interconnect trenches 5 provided in the
interconnect insulating film with the intermediary of a barrier
film 6 therebetween. An etching stopper film 8 composed of silicon
carbide (SiC) is then formed on the Cu interconnects 7 and the
SiO.sub.2 film 4. This etching stopper film 8 also functions as a
diffusion barrier film and an antioxidation film for the Cu.
[0011] Deposited on the etching stopper film 8 are a first
insulating film 9 composed of MSQ, i.e., a carbon-doped silicon
oxide film (SiOC film), and a second insulating film 10 composed of
PAE as an organic insulating film. The formation of the films 9 and
10 is followed by sequential deposition of a first-mask forming
layer 11 composed of SiO.sub.2, a second-mask forming layer 12
composed of silicon nitride (SiN), and a third-mask forming layer
13 composed of SiO.sub.2. Furthermore, a resist mask 14 having an
interconnect trench pattern is formed on the third-mask forming
layer 13.
[0012] Referring next to FIG. 7B, the third-mask forming layer
(SiO.sub.2) 13 (see FIG. 7A) is etched by dry etching that employs
the resist mask 14 (see FIG. 7A) as the etching mask, to thereby
form a third mask 13' having the interconnect trench pattern, which
is then followed by ashing removal of the resist mask 14.
[0013] Referring next to FIG. 7C, a resist mask 15 having a via
hole pattern is formed on the second-mask forming layer 12 and the
third mask 13'. The resist mask 15 is formed so that at least part
of apertures of the resist mask 15 overlaps with apertures of the
interconnect trench pattern formed in the third mask 13'.
[0014] Subsequently, as shown in FIG. 7D, the third mask
(SiO.sub.2) 13', the second-mask forming layer (SiN) 12 and the
first-mask forming layer (SiO.sub.2) 11 are etched by dry etching
that employs the resist mask 15 (see FIG. 7C) as the etching mask.
In addition, the second insulating film (PAE) 10 is also
perforated, which forms via holes 16 exposing the surface of the
first insulating film (SiOC) 9. The resist mask 15 is removed in
the etching of the second insulating film (PAE) 10, which is an
organic material. Even when the resist mask 15 is completely
removed during the perforation of the second insulating film 10,
the formation of the via holes 16 having a favorable aperture shape
are allowed due to the second-mask forming layer (SiN) 12 (see FIG.
7C) serving as the mask, since the second-mask forming layer 12 has
the pattern of the via holes 16.
[0015] Referring next to FIG. 7E, by dry etching with use of the
third mask (SiO.sub.2) 13' having the interconnect trench pattern
as the etching mask, the second-mask forming layer (SiN) 12 (see
FIG. 7D) having the via hole pattern is etched to thereby form a
second mask 12' having the interconnect trench pattern, and the
first insulating film 9 is etched to an intermediate thickness
thereof so that the via holes 16 are extended downward.
[0016] Referring next to FIG. 7F, by using the third mask
(SiO.sub.2) 13' (see FIG. 7E) and the second mask (SiN) 12' that
have the interconnect trench pattern, part of the first-mask
forming layer (SiO.sub.2) 11 remaining in the interconnect trench
region (see FIG. 7E) is removed to thereby form the first mask 11'
having the interconnect trench pattern. In this removal, the first
insulating film (SiOC) 9 remaining under the bottoms of the via
holes 16 is etched, so that the via holes 16 expose the etching
stopper film 8. The third mask 13' is removed in this etching
step.
[0017] Subsequently, as shown in FIG. 7G, the etching stopper film
8 exposed through the bottoms of the via holes 16 is etched so that
the via holes 16 are extended downward to reach the Cu
interconnects 7, and the second mask 12' (see FIG. 7F) is removed.
Thereafter, the second insulating film (PAE) 10 remaining under the
bottom of the interconnect trench pattern is etched with use of the
first mask (SiO.sub.2) 11' having the interconnect trench pattern
as the etching mask. Thus, the interconnect trench pattern provided
in the first mask 11' is extended downward, which results in the
formation of interconnect trenches 17 in the first mask 11' and the
second insulating film 10. Accordingly, the state is obtained in
which the interconnect trenches 17 communicate with the lower Cu
interconnects 7 by the via holes 16.
[0018] After the above-described steps, by posttreatment employing
chemicals and RF-sputtering treatment, etching fouling that remains
on sidewalls of the interconnect trenches 17 and the via holes 16
are removed, and modified layers in the surfaces of the Cu
interconnects 7 at the bottoms of the via holes 16 are
normalized.
[0019] Referring next to FIG. 7H, a barrier metal film 18 composed
of tantalum (Ta) is deposited by sputtering in a manner of covering
the inside walls of the interconnect trenches 17 and the via holes
16. Subsequently, a conductive film (not shown) composed of Cu is
deposited on the barrier metal film 18 by electrolytic plating or
sputtering in a manner of filling the interconnect trenches 17 and
the via holes 16. Thereafter, by using chemical mechanical
polishing (CMP), extra part of the conductive film and the barrier
metal film 18 unnecessary for the interconnect pattern is removed,
and upper part of the first mask 11' is also removed. Thus, vias 19
composed of Cu are formed in the via holes 16 while Cu
interconnects 20 are formed in the interconnect trenches 17, which
allows achievement of a dual damascene multilevel interconnect
structure. Moreover, an etching stopper film 21 composed of e.g.
SiC is formed on the Cu interconnects 20 and the first mask 11',
similarly to the etching stopper film 8 on the lower Cu
interconnects 7.
[0020] Use of this dual damascene method employing three layers of
etching masks eliminates the above-described technical restrictions
regarding a low-k material structure, and allows a manufacturing
method in which a load associated with resist patterning steps is
light.
[0021] Specifically, as shown in FIGS. 7A and 7C, reproduction
treatment of the resist masks 14 and 15 that are incompatible with
the product standard can be implemented on the third-mask forming
layer (SiO.sub.2) 13 and the second-mask forming layer (SiN) 12. In
addition, as described with reference to FIG. 7D, the removal of
the resist mask 15 for opening the via holes 16 can be carried out
simultaneously with the step of etching the second insulating film
(PAE) 10 to extend the via holes 16. Therefore, resist removal can
be implemented while suppressing damage to low-k material
films.
[0022] Furthermore, as shown in FIG. 7C, the via holes 16 are
formed through the third mask 13' having the interconnect trench
pattern. Therefore, when the resist mask 15 having the via hole
pattern is formed, the height of steps in the underlayer thereof is
as large as only the thickness of the third mask 13'. Therefore,
defocusing in exposure is suppressed, which can form a resist mask
having a highly accurate via hole pattern. Moreover, as shown in
FIG. 7D, since the via holes 16 are formed through the third mask
13' having the interconnect trench pattern, no variation in the
size of the via holes 16 arises even if misalignment between the
interconnect trenches 17 and the via holes 16 is caused.
[0023] In addition, as described with reference to FIG. 7G, when
the second insulating film (PAE) 10 is etched to form the
interconnect trenches 17, the etching of the second insulating film
10 is carried out on the first insulating film (SiOC) 9. Thus, a
high etching selection ratio can easily be ensured. Therefore, the
depth of the interconnect trenches 17 can easily be controlled
without providing an etching stopper film composed of a high
dielectric constant material such as an SiN film.
[0024] However, in the above-described dual damascene method, the
first mask 11', which remains among interconnects even after
completion of the device, is formed of an SiO.sub.2 film.
Therefore, the SiO.sub.2 film, which has a dielectric constant of
about 4, remains among the interconnects. Accordingly, even if an
organic insulating film such as PAE is used as a lower interconnect
insulating film to reduce the dielectric constant to some extent,
it is difficult to reduce the effective dielectric constant among
the interconnects. Thus, it is also difficult to reduce the
interconnect capacitance.
[0025] If in the above-described technique, an SiOC film (k=3.0) is
used in order to reduce the interconnect capacitance instead of the
SiO.sub.2 film 4 (k=4.1) serving as the insulating film among the
lower Cu interconnects 7 and instead of the SiO.sub.2 film (k=4.1)
of the first-mask forming layer 11 (see FIG. 7A) serving as the
insulating film among the upper Cu interconnects 20, the following
problem arises.
[0026] The problem will be described with reference to FIG. 8A to
FIG. 9. As shown in FIG. 8A, also when an SiOC film is used for the
layers 4 and 11, the manufacturing process employs the same steps
as those described with FIGS. 7A to 7E, i.e., until the step in
which the second mask 12' is formed and the via holes 16 are
extended downward partway across the first insulating film 9 with
use of the third mask 13' as the etching mask. The first-mask
forming layer 11 is formed to have a large thickness that includes
both the thickness for interconnects and the thickness of
sacrificial part to be removed in a CMP step to be carried out
later.
[0027] Referring next to FIG. 8B, the first-mask forming layer
(SiOC) 11 (see FIG. 8A) is etched to thereby form a first mask 11'
having an interconnect trench pattern. In this step, the first
insulating film (SiOC) 9 is also etched with the second insulating
film (PAE) 10 with the via hole pattern serving as the mask, and
therefore the via holes 16 are further extended downward so that
the etching stopper film (SiC) 8 is exposed. In this etching, the
etching selection ratio of SiOC to SiC (SiOC/SiC) is about 3. Since
the first-mask forming layer (SiOC) 11 has a large thickness, the
etching stopper film 8 is removed and thus the lower Cu
interconnects 7 are exposed. Accordingly, the surfaces of the Cu
interconnects 7 are susceptible to damage. In addition, in the
region in which misalignment between the Cu interconnect 7 and the
via hole 16 is caused, a hole A that reaches the PAE film 3 is
formed in the SiOC film 4.
[0028] In the step of forming the first mask 11', dry etching is
carried out by using the third mask (SiO.sub.2) 13' (see FIG. 8A)
having the interconnect trench pattern and the second mask (SiN)
12' as the etching mask. However, apertures of the interconnect
trench pattern formed in the first-mask forming layer (SiOC) 11
become wider than the intended size. This is because the etching
selection ratio of the first-mask forming layer 11 to the third and
second masks 13' and 12' serving as the etching mask is not
sufficiently high, and the first-mask forming layer 11 has a large
thickness. Therefore, the thicknesses of the third and second masks
13' and 12' are insufficient to adequately etch the first-mask
forming layer 11.
[0029] Referring next to FIG. 8C, under the above-described state,
the second insulating film (PAE) 10 is etched by etching that
employs the first mask 11' as the etching mask. Thus, the
interconnect trench pattern provided in the first mask 11' is
extended downward, which results in the formation of interconnect
trenches 17 in the first mask 11' and the second insulating film
10. Subsequently, the barrier metal film 18 is deposited to cover
the inside walls of the interconnect trenches 17 and the via holes
16, and then the conductive film 22 is formed on the barrier metal
film 18 in a manner of filling the interconnect trenches 17 and the
via holes 16.
[0030] Referring next to FIG. 9, by using CMP, extra part of the
conductive film 22 (see FIG. 8C) and the barrier metal film 18
unnecessary as the interconnect pattern is removed, and upper part
of the first mask 11' is also removed. Thus, vias 19 are formed in
the via holes 16 while Cu interconnects 20 are formed in the
interconnect trenches 17. Subsequently, an etching stopper film 21
is formed on the Cu interconnects 20 and the first mask 11'.
[0031] In the above-described manufacturing method, a void B is
generated in the vias 19 and the interconnects 20 due to burying
defects attributed to the hole A described with reference to FIG.
8B. Consequently, electromigration and stress migration due to the
void B arise in the use environment of the semiconductor device,
which deteriorates the interconnect reliability. In addition, if a
hole A' arising from widening of the hole A is generated in the
SiOC film 4 and the PAE film 3 due to the subsequent etching,
defects of voltage-withstanding characteristic of the interconnect
insulating film arises. As one approach for overcoming this
problem, increasing the thickness of the first insulating film 9 in
order to prevent the generation of the hole A is also possible.
However, this thickness increase leads to a higher embodiment ratio
of the via holes 16 formed in the first insulating film 9. Such a
high aspect ratio probably leads to insufficient burying of the
conductive film 22 (see FIG. 8C) into the via holes 16, which
results in conduction defects.
[0032] Furthermore, since apertures of interconnect trench pattern
of the first mask 11' are larger than the predetermined size, the
widths of the interconnect trenches 17 are also larger than the
predetermined size. Therefore, a sufficient voltage-withstanding
characteristic between adjacent interconnects cannot be ensured,
which lowers the yield of the semiconductor device. If in order to
overcome this problem, the third mask 13' (see FIG. 8A) is formed
to have a large thickness and then the first-mask forming layer 11
is etched with use of the third mask 13', the interconnect trench
pattern with its size error being suppressed can be formed.
However, since the via holes are extended downward in this etching
with the second insulating film 10 having the via hole pattern
serving as the mask, the first insulating film 9 and the etching
stopper film 8 are etched, which exposes the surfaces of the Cu
interconnects 7. In addition, the SiOC film 4, which is the lower
layer, is also etched.
[0033] Against the above-described background, there is a need for
the following manufacturing method of a semiconductor device and a
semiconductor device obtained through the method. Specifically, by
the method, the whole interlayer and interconnect insulating films
are allowed to keep a low dielectric constant. In addition, in
steps of forming interconnect trenches and via holes in the
insulating films, the interconnect trenches can be formed with
favorable processing controllability, without the occurrence of
exposure of lower interconnects and etching of lower interconnect
insulating films.
SUMMARY OF THE INVENTION
[0034] In order to solve the above-described problems, in a method
of manufacturing a semiconductor device according to a first
embodiment of the present invention, the following steps are
sequentially implemented. Specifically, initially, (a) a first
insulating film and a second insulating film are sequentially
formed over a substrate that includes a lower interconnect in a
region including a front surface of the substrate. The first
insulating film serves as an interlayer insulating film between
interconnect layers and is composed of a low-k material. The second
insulating film serves as an insulating film among interconnects
and is composed of a low-k material different from the material of
the first insulating film. Next, (b) a first-mask forming layer, a
second-mask forming layer, a third-mask forming layer, and a
fourth-mask forming layer are sequentially formed over the second
insulating film. The first-mask forming layer is composed of a
low-k material different from the material of the second insulating
film. The second-mask forming layer is composed of an insulating
material different from the material of the first-mask forming
layer. The third-mask forming layer is composed of an insulating
material different from the material of the second-mask forming
layer. The fourth-mask forming layer is composed of an insulating
material different from the third-mask forming layer. Subsequently,
(c) the fourth-mask forming layer is patterned to thereby form a
fourth mask having an interconnect trench pattern. Thereafter, (d)
a resist mask having a via hole pattern is formed on the fourth
mask and the third-mask forming layer. In addition, (e) with use of
the resist mask as an etching mask, the fourth mask, the third-mask
forming layer, the second-mask forming layer, and the first-mask
forming layer are etched, and then the second insulating film is
etched, to thereby open a via hole. Next, (f) with use of the
fourth mask as an etching mask, the third-mask forming layer is
etched to thereby form a third mask having the interconnect trench
pattern, and the first insulating film is etched to an intermediate
thickness of the first insulating film to thereby extend the via
hole downward. Subsequently, (g) with use of the fourth mask and
the third mask as an etching mask, the second-mask forming layer is
etched to thereby form a second mask having the interconnect trench
pattern, and the first insulating film that remains under the
bottom of the via hole is etched to thereby extend the via hole
downward so that the via hole reaches the substrate. The fourth
mask is removed as a result of the etching of the second-mask
forming layer. Next, (h) the first-mask forming layer is etched
with use of the third mask as an etching mask, to thereby form a
first mask having the interconnect trench pattern. Thereafter, (i)
after removal of the third mask, an interconnect trench is formed
in the second insulating film with use of the second mask as an
etching mask. In addition, (j) the second mask is removed after the
forming of the interconnect trench.
[0035] In addition, in a method of manufacturing a semiconductor
device according to a second embodiment of the present invention,
the following steps are sequentially implemented. Specifically,
initially, (a) a first insulating film and a second insulating film
are sequentially formed over a substrate that includes a lower
interconnect in a region including a front surface of the
substrate. The first insulating film serves as an interlayer
insulating film between interconnect layers and is composed of a
low-k material. The second insulating film serves as an insulating
film among interconnects and is composed of a low-k material
different from the material of the first insulating film. Next, (b)
a first-mask forming layer, a second-mask forming layer, a
third-mask forming layer, and a fourth-mask forming layer are
sequentially formed over the second insulating film. The first-mask
forming layer is composed of a low-k material different from the
material of the second insulating film. The second-mask forming
layer is composed of an insulating material different from the
material of the first-mask forming layer. The third-mask forming
layer is composed of an insulating material different from the
material of the second-mask forming layer. The fourth-mask forming
layer is composed of an insulating material different from the
third-mask forming layer. Subsequently, (c) the fourth-mask forming
layer, the third-mask forming layer, and the second-mask forming
layer are patterned to thereby form a via hole pattern in the
fourth-mask forming layer, the third-mask forming layer, and the
second-mask forming layer. Thereafter, (d) a resist mask having an
interconnect trench pattern is formed over the fourth-mask forming
layer having the via hole pattern. In addition, (e) the fourth-mask
forming layer is etched with use of the resist mask as an etching
mask, to thereby form a fourth mask having the interconnect trench
pattern. Next, (f) the first-mask forming layer is etched with
using, as an etching mask, the third-mask forming layer and the
second-mask forming layer that have the via hole pattern, to
thereby form the via hole pattern in the first-mask forming layer,
and the third-mask forming layer is etched with using the fourth
mask as an etching mask, to thereby form a third mask having the
interconnect trench pattern. Subsequently, (g) a via hole is opened
in the second insulating film with use of the second-mask forming
layer having the via hole pattern as an etching mask. Next, (h)
with use of the fourth mask and the third mask as an etching mask,
the second-mask forming layer is etched to thereby form a second
mask having the interconnect trench pattern, and the via hole is
extended downward partway across the first insulating film. The
fourth mask is removed as a result of the etching. Subsequently,
(i) with use of the third mask as an etching mask, the first-mask
forming layer is etched to thereby form a first mask having the
interconnect trench pattern, and the first insulating film that
remains under the bottom of the via hole is etched to thereby
extend the via hole downward so that the via hole reaches the
substrate. Thereafter, (j) after removal of the third mask, an
interconnect trench is formed in the second insulating film with
use of the second mask as an etching mask. In addition, (k) the
second mask is removed after the forming of the interconnect
trench.
[0036] In the manufacturing methods of a semiconductor device
according to the first and second embodiments, after the
interconnect trench is formed in the second insulating film, the
first mask is left on the second insulating film and serves as an
insulating film that defines the interconnect trench in association
with the second insulating film. The first insulating film, the
second insulating film, and the first mask are each formed of a
low-k material. Thus, the dielectric constant of the whole
interlayer and interconnect insulating films can be maintained at a
low value.
[0037] If after the formation of the interconnect trench in the
second insulating film, a conductive film is formed on the second
mask in a manner of filling the interconnect trench pattern of the
second and first masks, the interconnect trench, and the via hole,
and then extra part of the conductive film unnecessary as an
interconnect pattern is removed in addition to the second mask by
CMP, the second-mask forming layer serves as sacrificial part to be
removed by the CMP. Thus, the first-mask forming layer composed of
a low-k material is allowed to have a smaller thickness compared
with the case where the sacrificial part for the CMP is also
composed of a low-k material. This small thickness of the
first-mask forming layer suppresses the degree of downward
extension of the via hole when the first-mask forming layer is
etched to form the first mask, which prevents damage to lower
interconnects provided in the substrate due to exposure of the
lower interconnects. In addition, even when misalignment between
the lower interconnect and the via hole is caused, the etching of a
lower interconnect insulating film is suppressed. Thus, burying
defects, voltage-withstanding characteristic defects,
electromigration and stress migration attributed to holes due to
the etching are suppressed.
[0038] Furthermore, since the first-mask forming layer composed of
a low-k material is allowed to have a smaller thickness compared
with the case where the sacrificial part for the CMP is also
composed of a low-k material, the interconnect trench pattern can
be formed in the first-mask forming layer with favorable processing
controllability even if the etching selection ratios of the
first-mask forming layer to the second-mask and third-mask forming
layers, which serve as the etching mask, are not sufficiently
high.
[0039] According to a third embodiment of the present invention,
there is provided a semiconductor device having an insulating film
that includes a low-k material having a dielectric constant smaller
than the dielectric constant of silicon dioxide. The semiconductor
device includes a first insulating film that is composed of a low-k
material and is provided over a substrate, a second insulating film
that is provided on the first insulating film and is composed of a
low-k material different from the material of the first insulating
film, and a third insulating film that is provided on the second
insulating film and is composed of a low-k material different from
the material of the second insulating film. The semiconductor
device also includes a via that is provided in the first insulating
film and reaches the substrate, an interconnect that is provided in
the second insulating film and the third insulating film and
communicates with the via, and a thin-film fourth insulating film
that is provided on the whole or part of the third insulating film,
and is composed of an insulating material different from the
material of the third insulating film.
[0040] This semiconductor device is formed by the above-described
manufacturing methods of a semiconductor device. In the
semiconductor device, the first insulating film, the second
insulating film and the third insulating film, in which the via and
interconnect are provided, are each formed of a low-k material.
Therefore, the dielectric constant of the whole interlayer and
interconnect insulating films can be maintained at a low value.
[0041] As described above, according to the methods of
manufacturing a semiconductor device and the semiconductor device
obtained through any of the methods in accordance with the
embodiments of the present invention, the dielectric constant of
the whole interlayer and interconnect insulating films can be
maintained at a low value, and thus the interconnect capacitance
can be maintained at a low value. Accordingly, a high-performance
semiconductor device with its operational delays being suppressed
can be achieved. In addition, electromigration and stress migration
are suppressed, which can enhance the interconnect reliability.
Furthermore, the interconnect trench pattern can be formed with
favorable processing controllability, and therefore a semiconductor
device involving less size errors can be obtained, which prevents
lowering of the yield.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIGS. 1A to 1K are sectional views for explaining
manufacturing steps of a method of manufacturing a semiconductor
device according to a first embodiment of the present
invention;
[0043] FIG. 2 is a sectional view for explaining a method of
manufacturing a semiconductor device as a first modification of the
first embodiment;
[0044] FIG. 3 is a graph showing the interconnect capacitances of
semiconductor devices manufactured by the method according to the
first modification, as a function of the thickness of a remaining
second mask;
[0045] FIGS. 4A to 4K are sectional views for explaining
manufacturing steps of a method of manufacturing a semiconductor
device according to a second embodiment of the present
invention;
[0046] FIGS. 5A to 5M are sectional views for explaining
manufacturing steps of a method of manufacturing a semiconductor
device according to a third embodiment of the present
invention;
[0047] FIG. 6 is a graph showing the interconnect capacitances of
semiconductor devices according to a first working example of the
present invention, as a function of the thickness of an etching
stopper film;
[0048] FIGS. 7A to 7H are sectional views for explaining
manufacturing steps of a conventional method of manufacturing a
semiconductor device;
[0049] FIGS. 8A to 8C are sectional views for explaining problems
in the conventional method of manufacturing a semiconductor
device;
[0050] FIG. 9 is a sectional view for explaining the problems in
the conventional method of manufacturing a semiconductor
device;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0051] Embodiments of the present invention will be described in
detail below with reference to the accompanying drawings.
First Embodiment
[0052] The following embodiment example shows a method of
manufacturing a semiconductor device according to a first
embodiment of the present invention. The first embodiment relates
to the formation of a dual damascene structure by a trench-first
approach, in which the formation of a mask pattern for forming
interconnect trenches (interconnect trench pattern) precedes the
formation of a mask pattern for forming via holes (via hole
pattern). The first embodiment will be described below with
reference to FIGS. 1A to 1K, which are sectional views illustrating
manufacturing steps. The same elements in FIGS. 1A to 1K as those
in FIG. 7A to FIG. 9 for the above-described manufacturing method
as background techniques are given the same numerals.
[0053] Referring initially to FIG. 1A, over a base silicon
substrate 1 having thereon element regions and so on (not shown), a
multilayer film of a PAE film 3 (k=2.3) with a thickness of 90 nm
and an SiOC film (MSQ) 4 (k=3.0) with a thickness of 140 nm is
deposited as an interconnect insulating film with the intermediary
of a base insulating film 2 between the substrate 1 and the
multilayer film. Subsequently, interconnect trenches 5 are formed
in the interconnect insulating film, and then buried interconnects
composed of e.g. Cu (Cu interconnects) 7 are formed on barrier
metals 6 in the interconnect trenches 5. The Cu interconnects 7 are
designed to have an interconnect thickness of 140 nm. In the step
of forming the buried interconnects, the SiOC film 4 is polished by
CMP by 90 nm in thickness.
[0054] An etching stopper film 8 composed of e.g. SiC is then
formed on the Cu interconnects 7 and the SiOC film 4. This etching
stopper film 8 also functions as a diffusion barrier film and an
antioxidation film for the Cu interconnects 7. The etching stopper
film 8 prevents exposure of the Cu interconnects 7 and etching of
the SiOC film 4 when a first insulating film formed on the etching
stopper film 8 is etched to form via holes in later steps. The
etching stopper film 8 is formed of SiC, which has a dielectric
constant of 5. Therefore, in order to keep a low dielectric
constant between interconnect layers, it is preferable that the
thickness of the etching stopper film 8 is as small as possible, as
long as the diffusion of Cu and etching of the lower film 4 can be
prevented. In the present embodiment, the etching stopper film 8
has a thickness of e.g. 35 nm.
[0055] Formed on the etching stopper film 8 is a first insulating
film 9 composed of a low-k material as an interlayer insulating
film. Formed in the present embodiment is the first insulating film
9 that has a thickness of 90 nm and is formed of MSQ, i.e.,
carbon-doped silicon oxide (SiOC), which is an inorganic low-k
material and has a dielectric constant of 2.3. Note that HSQ may be
used instead of the MSQ for the first insulating film 9.
[0056] Formed on the first insulating film 9 is a second insulating
film 10 composed of a low-k material that is different from the
material of the first insulating film 9. This example employs an
organic polymer as an organic low-k material for the second
insulating film 10. For example, the second insulating film 10 has
a thickness of 90 nm and is composed of polyarylether (PAE), which
has a dielectric constant of 2.3. Note that benzocyclobutene (BCB)
or fluorocarbon (CF.sub.x) may be used instead of the PAE for the
second insulating film 10.
[0057] The deposition of the second insulating film 10 is followed
by sequential formation of a first-mask forming layer 31, a
second-mask forming layer 32, a third-mask forming layer 33, and a
fourth-mask forming layer 34.
[0058] The first-mask forming layer 31 is composed of e.g. an
inorganic low-k material similar to the material of the first
insulating film 9. Specifically, it is formed of e.g. an SiOC film
(MSQ) having a dielectric constant of 3.0 and has a thickness of 50
nm. The first-mask forming layer 31 remains as an insulating film
among interconnects formed in interconnect trenches even after the
completion of the manufacturing process as described later.
Therefore, it is formed of a low-k material in order to keep the
dielectric constant of the interconnect insulating film at a low
value.
[0059] The second-mask forming layer 32 is composed of e.g. a
silicon-based insulating material that is different from the
material of the first-mask forming layer (SiOC film) 31. It is
preferable for the second-mask forming layer 32 to be composed of,
of the silicon-based insulating materials, a material that allows
processing of the first-mask forming layer 31 by reactive ion
etching that employs a mask formed of the second-mask forming layer
32 as the etching mask. The second-mask forming layer 32 serves as
sacrificial part to be removed in a later CMP step. In the present
embodiment, the second-mask forming layer 32 composed of SiO.sub.2
is formed to have a thickness of 90 nm.
[0060] The third-mask forming layer 33 is composed of a
silicon-based insulating material different from the material of
the second-mask forming layer 32. It is preferable for the
third-mask forming layer 33 to be composed of, of the silicon-based
insulating materials, a material that allows processing of the
second-mask forming layer 32 by reactive ion etching that employs a
mask formed of the third-mask forming layer 33 as the etching mask.
Examples of the materials of the third-mask forming layer 33
include SiN and SiC. In the present embodiment, the third-mask
forming layer 33 composed of SiN is formed to have a thickness of
50 nm.
[0061] The fourth-mask forming layer 34 is composed of a
silicon-based insulating material different from the material of
the third-mask forming layer 33. It is preferable for the
fourth-mask forming layer 34 to be composed of, of the
silicon-based insulating materials, a material that allows
processing of the third-mask forming layer 33 by reactive ion
etching that employs a mask formed of the fourth-mask forming layer
34 as the etching mask. In the present embodiment, the fourth-mask
forming layer 34 composed of SiO.sub.2 is formed to have a
thickness of 50 nm.
[0062] After the mask-forming layers of the four-layer structure
are formed in this manner, a resist mask 14 having a interconnect
trench pattern is formed on the fourth-mask forming layer 34.
[0063] Referring next to FIG. 1B, the fourth-mask forming layer
(SiO.sub.2) 34 (see FIG. 1A) is etched by dry etching that employs
the resist mask 14 (see FIG. 1A) as the etching mask, to thereby
form a fourth mask (SiO.sub.2) 34' having the interconnect trench
pattern. In this dry etching, a typical magnetron etching apparatus
is used, and e.g. octafluorobutane (C.sub.4F.sub.8), carbon oxide
(CO), and argon (Ar) are employed as the etching gas. The gas flow
ratio (C.sub.4F.sub.8:CO:Ar) is set to 1:5:20, and the bias power
is set to 1200 W. Under this etching condition, the etching
selection ratio of SiO.sub.2 to SiN (SiO.sub.2/SiN) is 10 or more.
Therefore, the etching of the fourth-mask forming layer 34 can be
carried out almost without etching the third-mask forming layer
(SiN) 33, which serves as the underlayer in the etching.
[0064] After the fourth mask 34' is thus formed, ashing treatment
based on oxygen (O.sub.2) plasma and treatment employing an organic
amine chemical are implemented for example, to thereby completely
remove the resist mask 14 and residual fouling produced in the
etching treatment.
[0065] Referring next to FIG. 1C, a resist mask 15 having a via
hole pattern is formed on the third-mask forming layer 33 and the
fourth mask 34'. At this time, the resist mask 15 is patterned so
that at least part of apertures of the via hole pattern provided in
the resist mask 15 overlaps with apertures of the fourth mask
34'.
[0066] Referring next to FIG. 1D, by dry etching that employs the
resist mask 15 (see FIG. 1C) as the etching mask, the fourth mask
34', the third-mask forming layer 33, the second-mask forming layer
32 and the first-mask forming layer 31 are etched, and then the
second insulating film 10 is also etched. Thus, via holes 16
exposing the first insulating film 9 are formed.
[0067] In the dry etching for the layers from the fourth mask 34'
to the first-mask forming layer 31, a typical magnetron etching
apparatus is used and e.g. C.sub.4F.sub.8 and Ar are employed as
the etching gas. The gas flow ratio (C.sub.4F.sub.8:Ar) is set to
1:4, and the bias power is set to 400 W.
[0068] In the present embodiment, the etching selection ratio among
SiO.sub.2, SiN and SiOC is about 1 under this etching condition.
Therefore, simply by one etching step, four layers of the
insulating films, i.e., the layers from the fourth mask 34' to the
first-mask forming layer 31 are collectively etched to form the via
holes 16. Alternatively, depending on the resist selection ratio,
etching bias and so on, the layers from the fourth mask 34' to the
first-mask forming layer 31 may be etched sequentially by using two
or more etching steps.
[0069] In the subsequent etching for the second insulating film
(PAE) 10, a typical high-density plasma etching apparatus is used
and e.g. ammonium (NH.sub.3) is employed as the etching gas. The RF
power is set to 150 W. Under this etching condition, the etching
rate of the resist mask 15 is almost the same as that of the second
insulating film 10. Therefore, in the etching of the second
insulating film 10, the thickness of the resist mask 15 gradually
decreases and finally the resist mask 15 is completely removed.
After the resist mask 15 is thus completely removed, the third-mask
forming layer 33 having the via hole pattern serves as the etching
mask, which allows achievement of favorable aperture shapes of the
via holes 16. Under the etching condition of the etching for the
second insulating film 10, the etching selection ratios of the
second insulating film (PAE) 10 to SiN, SiO.sub.2 and SiOC are all
100 or more.
[0070] Referring next to FIG. 1E, the third-mask forming layer
(SiN) 33 (see FIG. 1D) is etched by dry etching that employs the
fourth mask (SiO.sub.2) 34' having the interconnect trench pattern
as the etching mask. Thus, a third mask 33' having the interconnect
trench pattern is formed.
[0071] In this dry etching, a typical magnetron etching apparatus
is used and difluoromethane (CH.sub.2F.sub.2), oxygen (O.sub.2) and
argon (Ar) are employed as the etching gas for example. The gas
flow ratio (CH.sub.2F.sub.2:O.sub.2:Ar) is set to 1:1:10, and the
bias power is set to 300 W. Under this etching condition, the
etching selection ratio of SiN to SiO.sub.2 (SiN/SiO.sub.2) is
about 2 to 3. Therefore, although the thickness of the fourth mask
(SiO.sub.2) 34' decreases to some extent in the etching, the
initial thickness of about 50 nm of the fourth mask 34' includes a
sufficient margin to etch the third-mask forming layer (SiN) 33
with a thickness of 50 nm to thereby form the interconnect trench
pattern in the third-mask forming layer 33.
[0072] In addition, under this etching condition, the etching
selection ratio of SiOC to SiN (SiOC/SiN) is slightly lower than 1.
Therefore, since the third-mask forming layer (SiN) 33 with a
thickness of 50 nm is etched with consideration for requisite over
etching therefore, the via holes 16 are extended downward by about
50 nm from the surface of the first insulating film (SiOC) 9.
[0073] Subsequently, as shown in FIG. 1F, the second-mask forming
layer (SiO.sub.2) 32 (see FIG. 1E) is etched by dry etching in
which the fourth mask (SiO.sub.2) 34' (see FIG. 1E) and the third
mask (SiN) 33' are used as the etching mask. Thus, a second mask
32' having the interconnect trench pattern is formed.
[0074] In this dry etching, a typical magnetron etching apparatus
is used and C.sub.4F.sub.8, O.sub.2 and Ar are employed as the
etching gas for example. The gas flow ratio
(C.sub.4F.sub.8:O.sub.2:Ar) is set to 2:1:80, and the bias power is
set to 800 W. In this etching, the fourth mask (SiO.sub.2) 34' is
also etched in step with the etching of the second-mask forming
layer 32 since the fourth mask (SiO.sub.2) 34' and the second-mask
forming layer (SiO.sub.2) 32 are formed of the same material
(SiO.sub.2). Under the above-described etching condition, the
etching selection ratio of SiO.sub.2 to SiN (SiO.sub.2/SiN) is
about 5. Therefore, although the thickness of the third mask (SiN)
33' decreases to some extent in the etching, the initial thickness
of about 50 nm of the third mask (SiN) 33' includes a sufficient
margin to etch the second-mask forming layer (SiO.sub.2) 32 with a
thickness of 90 nm to thereby form the interconnect trench pattern
in the second-mask forming layer (SiO.sub.2) 32. In addition, the
etching selection ratio of SiO.sub.2 to SiOC (SiO.sub.2/SiOC) is
about 1.5 in this etching. According to this etching selection
ratio, the via holes 16 are further extended downward with the
first-mask forming layer (SiOC) 31 having the via hole pattern
serving as the mask, and thus the etching stopper film (SiC) 8 is
exposed. Since the etching selection ratio of SiO.sub.2 to SiC
(SiO.sub.2/SiC) is about 10 under the above-described etching
condition, the etching stopper film (SiC) 8 is hardly etched.
[0075] Referring next to FIG. 1G, the first-mask forming layer
(SiOC) 31 (see FIG. 1F) is etched with using the third mask (SiN)
33' having the interconnect trench pattern. Thus, a first mask 31'
having the interconnect trench pattern is formed.
[0076] In this dry etching, a typical magnetron etching apparatus
is used and e.g. C.sub.4F.sub.8, Ar and nitrogen (N.sub.2) are
employed as the etching gas. The gas flow ratio
(C.sub.4F.sub.8:Ar:N.sub.2) is set to 1:200:4, and the bias power
is set to 600 W. Under this etching condition, the etching
selection ratio of SiOC to SiN (SiOC/SiN) is about 3. Before this
etching, the thickness of the third mask (SiN) 33' has been
decreased to about 30 nm in the etching step for the second mask
32' described with reference to FIG. 1F. However, since the etching
selection ratio SiOC/SiN is 3, this thickness of about 30 nm of the
third mask (SiN) 33' includes a sufficient margin to form the
interconnect trench pattern in the first-mask forming layer (SiOC)
31 with a thickness of 50 nm. In addition, since the etching
selection ratio of SiOC to SiC (SiOC/SiC) is about 3, the via holes
16 are extended downward by about 20 nm from the surface of the
etching stopper film 8. However, since the etching stopper film 8
has a thickness of 35 nm, the lower Cu interconnects 7 are not
exposed.
[0077] Referring next to FIG. 1H, the etching stopper film 8
remaining under the bottoms of the via holes 16 and the third mask
(SiN) 33' (see FIG. 1G) are etch-removed. In this dry etching, a
typical magnetron etching apparatus is used and CH.sub.2F.sub.2,
O.sub.2 and Ar are employed as the etching gas for example. The gas
flow ratio (CH.sub.2F.sub.2:O.sub.2:Ar) is set to 2:1:5, and the
bias power is set to 100 W.
[0078] Subsequently, as shown in FIG. 1I, the second insulating
film (PAE) 10 remaining under the bottom of the interconnect trench
pattern in the first mask 31' is etched with use of the second mask
(SiO.sub.2) 32' as the etching mask. Thus, the interconnect trench
pattern formed in the first mask 31' is extended downward, which
results in the formation of interconnect trenches 17 in the second
mask 32', the first mask 31' and the second insulating film 10.
Accordingly, a state is achieved in which the interconnect trenches
17 communicate with the lower Cu interconnects 7 by the via holes
16.
[0079] In the present embodiment, the interconnect trench
processing for the second insulating film 10 is carried out after
the etching stopper film 8 and the third mask 33' are removed.
Alternatively, the interconnect trench processing for the second
insulating film 10 may precede the removal of the etching stopper
film 8 and the third mask 33'.
[0080] In the etching for the second insulating film 10, a typical
high-density plasma etching apparatus is used and e.g. NH.sub.3 is
employed as the etching gas. The RF power is set to 150 W. Under
this etching condition, the etching selection ratio of PAE to SiOC
(PAE/SiOC) is 100 or more. This etching selection ratio prevents
thickness reduction of the first insulating film (SiOC) 9, which is
the underlayer in the etching, and thus allows the downward
extension of the interconnect trenches with favorable
controllability and no variation in trench depth. In addition, this
etching selection ratio suppresses the etching of the SiOC film 4
in the region in which misalignment between the via hole 16 and the
lower Cu interconnect 7 is caused.
[0081] After the above-described steps, by posttreatment employing
chemicals and RF-sputtering treatment, etching fouling that remains
on sidewalls of the interconnect trenches and via holes are
removed, and modified Cu layers at the bottoms of the via holes are
converted to normal Cu layers.
[0082] Thereafter, as shown in FIG. 1J, a barrier metal film 18
composed of e.g. Ta is deposited by sputtering in a manner of
covering the inside walls of the interconnect trenches 17 and the
via holes 16. Subsequently, a conductive film 22 composed of e.g.
Cu is deposited on the barrier metal film 18 by electrolytic
plating or sputtering in a manner of filling the interconnect
trenches 17 and the via holes 16. Thus, the interconnect trenches
17 and the via holes 16 are simultaneously filled.
[0083] Referring next to FIG. 1K, by using CMP, extra part of the
conductive film 22 (see FIG. 1J) and the barrier metal film 18
unnecessary as the interconnect pattern is removed, and the whole
second mask 32' is also removed. Thus, vias 19 are formed in the
via holes 16 while Cu interconnects 20 are formed in the
interconnect trenches 17. Moreover, an etching stopper film 21
composed of e.g. SiC is formed on the Cu interconnects 20 and the
first mask 31', similarly to the etching stopper film 8 on the
lower Cu interconnects 7. Subsequent repetition of the steps from
the forming step of the first insulating film 9 described with FIG.
1A to the step described with FIG. 1K allows the formation of a
multilevel interconnect structure based on a dual damascene
structure.
[0084] According to the above-described manufacturing method of a
semiconductor device and a semiconductor device obtained through
this method, the first mask 31' is left on the second insulating
film 10, and serves as a third insulating film that defines the
interconnect trenches 17 in association with the second insulating
film 10. The first insulating film 9, the second insulating film
10, and the first mask 31' are each formed of a low-k material.
Thus, the dielectric constant of the whole interlayer and
interconnect insulating films can be maintained at a low value.
Therefore, the interconnect capacitance can be maintained at a low
value. Accordingly, a high-performance semiconductor device with
its operational delays being suppressed can be achieved.
[0085] Since the second mask 32' in addition to extra part of the
conductive film 22 and the barrier metal film 18 unnecessary as the
interconnect pattern is removed by CMP until the surface of the
first mask 31' is exposed, the second-mask forming layer 32 serves
as sacrificial part to be removed by the CMP. Thus, the first-mask
forming layer 31 composed of a low-k material is allowed to have a
smaller thickness compared with the case where the sacrificial part
for the CMP is also composed of a low-k material. Accordingly, the
downward extension of the via holes 16 is suppressed in the step of
etching the first-mask forming layer 31 to form the first mask 31',
and thus the exposure of the Cu interconnects 7 is prevented, which
avoids damage to the Cu interconnects 7. In addition, even when
misalignment between the Cu interconnect 7 and the via hole 16 is
caused, the etching of the SiOC film 4 is suppressed. Thus,
troubles in filling the via holes 16 attributed to the etching of
the SiOC film 4, and electromigration and stress migration due to
the filling troubles are avoided. The interconnect reliability
therefore can be enhanced.
[0086] Furthermore, since the first-mask forming layer 31 is
allowed to have a small thickness, the interconnect trench pattern
of the first mask 31' can be formed with favorable processing
controllability by use of the third mask 33' as the etching mask.
Accordingly, a semiconductor device involving less size errors can
be obtained, which prevents lowering of the yield.
[0087] It should be noted that the present invention is not limited
to the above-described embodiment, in which Cu is used as the
material of the interconnects and vias, but any other conductive
material is also available.
(First Modification)
[0088] In the above description, the whole second mask 32' is
removed by CMP. Alternatively, as shown in FIG. 2, the thin-film
second mask 32' may remain on the entire first mask 31'. In this
structure, the first mask 31' serves as a third insulating film
that defines the interconnect trenches 17, while the second mask
32' serves as a fourth insulating film that also defines the
interconnect trenches 17.
[0089] FIG. 3 is a graph showing the interconnect capacitance of
the structure of FIG. 2 as a function of the thickness of the
second mask 32' (the fourth insulating film) that remains on the
first mask 31' (the third insulating film) with a thickness of 50
nm. In the graph, the interconnect capacitances are plotted with
the thickness of the second mask 32' being changed from 0 nm to 20
nm with an increment of 5 nm. The semiconductor device in which the
thickness of the second mask 32' (see FIG. 2) is 0 is obtained
through the same method as that of the first embodiment. Note that
the interconnect capacitances in this graph are indicated as the
ratio with respect to the interconnect capacitance of the
semiconductor device having a conventional structure shown in FIG.
7H as a background technique. That is, the interconnect capacitance
of the conventional structure is defined as 1.
[0090] This graph shows that, when the thickness of the second mask
32' is 20 nm or smaller, an interconnect capacitance smaller by 3
to 7% than that of the semiconductor device with the conventional
structure is obtained.
[0091] In the first modification, the second mask 32' remains on
the entire first mask 31' as shown in FIG. 2. Another modification,
however, is also applicable in which the second mask 32' remains on
part of the first mask 31'. Even in this modification, polishing
can be carried out without involving problems about the flatness
and so on, if the polishing selection ratio of SiO.sub.2 to SiOC in
CMP is set to about 1.
Second Embodiment
[0092] A method of manufacturing a semiconductor device according
to a second embodiment of the present invention will be described
below with reference to FIGS. 4A to 4K, which are sectional views
illustrating manufacturing steps. The same elements in the second
embodiment as those in the first embodiment are given the same
numerals, and detailed description thereof will be omitted.
[0093] Referring initially to FIG. 4A, in the second embodiment,
the manufacturing process is advanced in the same way as the first
embodiment until the step of forming Cu interconnects 7 in a PAE
film 3 and an SiOC film 4 after sequential deposition of the PAE
film 3 and the SiOC film 4 over a substrate 1 with the intermediary
of a base insulating film 2 therebetween.
[0094] Subsequently, a first etching stopper film 8a and a second
etching stopper film 8b are sequentially formed on the Cu
interconnects 7 and the SiOC film 4. The first etching stopper film
8a is composed of SiC and has a thickness of 35 nm for example. The
second etching stopper film 8b is composed of such a material that
the second etching stopper film 8b is less susceptible to being
etched than the first etching stopper film 8a when via holes are
formed in a first insulating film 9 on the second etching stopper
film 8b in a later step.
[0095] In the present embodiment, the second etching stopper film
8b is formed of an SiO.sub.2 film (SR--SiO.sub.2 film) of which
silicon content is higher than that of an SiO.sub.2 film deposited
by normal plasma-enhanced CVD (PECVD). The dielectric constant of
the SR--SiO.sub.2 film is 4.3. This SR--SiO.sub.2 film is formed by
increasing the amount of silicon-containing components in the
film-deposition gas in PECVD. In the deposition of the
SR--SiO.sub.2 film, a parallel plasma PECVD apparatus is used, and
silane (SiH.sub.4), dinitrogen monoxide (N.sub.2O) and N.sub.2 are
used as the film-deposition gas. The gas flow ratio
(SiH.sub.4:N.sub.2O:N.sub.2) is set to 1:17:5, and the RF power and
pressure are set to 600 W and 350 Pa, respectively. Whether or not
the SR--SiO.sub.2 film is formed can be confirmed by the refractive
index of the deposited film. Specifically, the refractive index of
a normal SiO.sub.2 film is 1.46, while that of the SR--SiO.sub.2
film is 1.5 or higher.
[0096] Since the dielectric constant of the SR--SiO.sub.2 is 4.3,
it is preferable for the SR--SiO.sub.2 film to have a thickness of
20 nm or smaller in order to reduce the dielectric constant of the
entire semiconductor device. A thickness of 20 nm or smaller allows
the interconnect capacitance of the formed semiconductor device to
be maintained at a low value. In the present embodiment, the second
etching stopper film 8b composed of an SR--SiO.sub.2 film is formed
to have a thickness of 10 nm.
[0097] Deposited on the second etching stopper film 8b is the first
insulating film 9 composed of e.g. SiOC and having a thickness of
80 nm as an interlayer insulating film. On the first insulating
film 9, a second insulating film 10 composed of e.g. PAE and having
a thickness of 90 nm is formed.
[0098] The deposition of the second insulating film 10 is followed
by sequential formation of a first-mask forming layer 31, a
second-mask forming layer 32, a third-mask forming layer 33 and a
fourth-mask forming layer 34. The materials of the first- to
fourth-mask forming layers 31 to 34 are the same as those in the
first embodiment. In contrast, the thicknesses of the layers 31 to
34 are different from those in the first embodiment.
[0099] Specifically, the first-mask forming layer 31 on the second
insulating film (PAE) 10 is composed of e.g. SiOC and has a
thickness of 70 nm. In the present embodiment, interconnects having
a interconnect thickness of 140 nm are formed in the first-mask
forming layer 31 with a thickness of 70 nm and the second
insulating film 10 with a thickness of 90 nm as described later.
Therefore, the upper part with a thickness of 20 nm in the
first-mask forming layer 31 serves as sacrificial part to be
removed in a later CPM step.
[0100] The second-mask forming layer 32 is composed of SiO.sub.2
and has a thickness of 70 nm. The second-mask forming layer 32 has
a thickness smaller by 20 nm than that in the first embodiment
since the upper part of the first-mask forming layer 31 serves as
sacrificial part for CMP as described above. The third-mask forming
layer 33 is composed of SiN and is 50 nm in thickness. The
fourth-mask forming layer 34 is composed of SiO.sub.2 and is 50 nm
in thickness.
[0101] After the mask-forming layers of the four-layer structure
are formed in this manner, a resist mask 14 having a interconnect
trench pattern is formed on the fourth-mask forming layer 34.
[0102] Referring next to FIG. 4B, the fourth-mask forming layer
(SiO.sub.2) 34 (see FIG. 4A) is etched by dry etching that employs
the resist mask 14 (see FIG. 4A) as the etching mask, to thereby
form a fourth mask 34' having the interconnect trench pattern. The
etching condition of this etching is the same as that in the first
embodiment. Subsequently, ashing treatment based on O.sub.2 plasma
and treatment employing an organic amine chemical are implemented
for example, to thereby completely remove the resist mask 14 and
residual fouling produced in the etching treatment.
[0103] Referring next to FIG. 4C, a resist mask 15 having a via
hole pattern is formed on the third-mask forming layer 33 and the
fourth mask 34'. At this time, the resist mask 15 is patterned so
that at least part of apertures of the via hole pattern provided in
the resist mask 15 overlaps with apertures of the fourth mask
34'.
[0104] Referring next to FIG. 4D, by dry etching that employs the
resist mask 15 (see FIG. 4C) as the etching mask, the fourth mask
34', the third-mask forming layer 33, the second-mask forming layer
32 and the first-mask forming layer 31 are etched, and then the
second insulating film 10 is also etched. Thus, via holes 16
exposing the first insulating film 9 are formed. This etching
employs the same etching condition as that in the first embodiment.
The resist mask 15 is removed in the etching of the second
insulating film (PAE) 10.
[0105] Referring next to FIG. 4E, the third-mask forming layer
(SiN) 33 (see FIG. 4D) is etched by dry etching in which the fourth
mask (SiO.sub.2) 34' having the interconnect trench pattern is used
as the etching mask. Thus, a third mask 33' having the interconnect
trench pattern is formed.
[0106] Subsequently, as shown in FIG. 4F, the second-mask forming
layer (SiO.sub.2) 32 (see FIG. 4E) is etched by dry etching in
which the fourth mask (SiO.sub.2) 34' (see FIG. 4E) and the third
mask (SiN) 33' having the interconnect trench pattern are used as
the etching mask. Thus, a second mask 32' having the interconnect
trench pattern is formed.
[0107] This dry etching employs the same etching condition as that
in the first embodiment. In this etching, the fourth mask 34' is
also etched in step with the etching of the second-mask forming
layer 32 since the fourth mask (SiO.sub.2) 34' and the second-mask
forming layer 32 (SiO.sub.2) are formed of the same material
(SiO.sub.2). The etching selection ratio of SiO.sub.2 to SiN
(SiO.sub.2/SiN) is about 5 in this etching. Therefore, although the
thickness of the third mask (SiN) 33' decreases to some extent in
the etching, the initial thickness of about 50 nm of the third mask
33' includes a sufficient margin to etch the second-mask forming
layer (SiO.sub.2) 32 (see FIG. 4E) with a thickness of 70 nm to
thereby form the interconnect trench pattern in the second-mask
forming layer 32. As a result of this etching, the thickness of the
third mask 33' decreases to about 35 nm.
[0108] In addition, the etching selection ratio of SiO.sub.2 to
SiOC (SiO.sub.2/SiOC) is about 1.5 in this etching. According to
this etching selection ratio, the via holes 16 are further extended
downward with the first-mask forming layer 31 having the via hole
pattern serving as the etching mask, and thus the second etching
stopper film (SR--SiO.sub.2) 8b is exposed. Moreover, since the
etching selection ratio of SiO.sub.2 to SR--SiO.sub.2
(SiO.sub.2/SR--SiO.sub.2) is about 4, the SR--SiO.sub.2 film is
etched by about 7 nm in thickness.
[0109] Referring next to FIG. 4G, the first-mask forming layer
(SiOC) 31 (see FIG. 4F) is etched with using the third mask (SiN)
33' having the interconnect trench pattern as the etching mask.
Thus, a first mask (SiOC) 31' having the interconnect trench
pattern is formed.
[0110] When this dry etching employs the same etching condition as
that in the first embodiment, the etching selection ratio of SiOC
to SiN (SiOC/SiN) is about 3. Before this etching, the thickness of
the third mask (SiN) 33' has been decreased to about 35 nm in the
step of forming the second mask 32' described with reference to
FIG. 4F. However, since the etching selection ratio SiOC/SiN is 3,
this thickness of about 30 nm of the third mask (SiN) 33' includes
a sufficient margin to form the interconnect trench pattern in the
first-mask forming layer (SiOC) 31 with a thickness of 70 nm.
Moreover, in this etching, the etching selection ratio of SiOC to
SR--SiO.sub.2 (SiOC/SR--SiO.sub.2) is 5, and the etching selection
ratio of SiOC to SiC (SiOC/SiC) is 3. Therefore, the via holes 16
penetrate the second etching stopper film 8b, and are extended
downward by about 20 nm from the surface of the first etching
stopper film 8a. However, since the first etching stopper film 8a
has a thickness of 35 nm, exposure of the lower Cu interconnects 7
is avoided.
[0111] The subsequent steps are carried out in the same way as the
first embodiment. Specifically, referring next to FIG. 4H, the
third mask 33' (see FIG. 4G) and the first etching stopper film 8a
remaining under the bottoms of the via holes 16 are
etch-removed.
[0112] Subsequently, as shown in FIG. 4I, the second insulating
film (PAE) 10 remaining under the bottom of the interconnect trench
pattern in the first mask (SiO.sub.2) 31' is etched with use of the
second mask (SiO.sub.2) 32' as the etching mask. Thus, the
interconnect trench pattern formed in the first mask 31' is
extended downward, which results in the formation of interconnect
trenches 17 in the second mask 32', the first mask 31' and the
second insulating film 10.
[0113] After the above-described steps, by posttreatment employing
chemicals and RF-sputtering treatment, etching fouling that remains
on sidewalls of the interconnect trenches 17 and the via holes 16
are removed, and modified Cu layers at the bottoms of the via holes
16 are converted to normal Cu layers.
[0114] Thereafter, as shown in FIG. 4J, a barrier metal film 18 is
deposited by sputtering in a manner of covering the inside walls of
the interconnect trenches 17 and the via holes 16. Subsequently, a
conductive film 22 composed of Cu is deposited on the barrier metal
film 18 by electrolytic plating or sputtering in a manner of
filling the interconnect trenches 17 and the via holes 16. Thus,
the interconnect trenches 17 and the via holes 16 are
simultaneously filled.
[0115] Referring next to FIG. 4K, by using CMP, extra part of the
conductive film 22 (see FIG. 4J) and the barrier metal film 18
unnecessary as the interconnect pattern is removed. In addition,
the whole second mask 32' and upper part of the first mask 31' are
also removed. Thus, vias 19 are formed in the via holes 16 while Cu
interconnects 20 are formed in the interconnect trenches 17.
Moreover, an etching stopper film 21 composed of SiC is formed on
the Cu interconnects 20 and the first mask 31', similarly to the
etching stopper film 8 on the lower Cu interconnects 7.
Accordingly, a multilevel interconnect structure based on a dual
damascene structure can be achieved.
[0116] According to the above-described manufacturing method of a
semiconductor device, the first mask 31' is left on the second
insulating film 10, and serves as a third insulating film that
defines the interconnect trenches in association with the second
insulating film 10. Since the first insulating film 9, the second
insulating film 10 and the first mask 31' are each formed of a
low-k material, the second embodiment can offer the same advantages
as those of the first embodiment.
[0117] Moreover, in the present embodiment, the whole second mask
32' and upper part of the first mask 31' in addition to extra part
of the conductive film 22 unnecessary as the interconnect pattern
are removed by CMP. Thus, the second mask 32', which has a high
dielectric constant, can surely be removed. This ensured removal of
the second mask 32' facilitates control of the dielectric constant
compared with the case where polishing residues of the second mask
32' partially remain.
[0118] In addition, the existence of the second etching stopper
film 8b between the first etching stopper film 8a and the first
insulating film 9 can prevent exposure of the lower Cu
interconnects 7 and etching of the SiOC film 4 more surely.
[0119] Note that features of the above-described modifications of
the first embodiment are available also in the second
embodiment.
Third Embodiment
[0120] A method of manufacturing a semiconductor device according
to a third embodiment of the present invention will be described
below with reference to FIGS. 5A to 5M, which are sectional views
illustrating manufacturing steps. The third embodiment relates to
the formation of a dual damascene structure by a via-first
approach, in which the formation of a mask pattern for forming via
holes (via hole pattern) precedes the formation of a mask pattern
for forming interconnect trenches (interconnect trench pattern).
The same elements in the third embodiment as those in the first
embodiment are given the same numerals, and detailed description
thereof will be omitted.
[0121] Referring initially to FIG. 5A, a PAE film 3 and an SiOC
film 4 are sequentially deposited over a substrate 1 with the
intermediary of a base insulating film 2 therebetween, and then Cu
interconnects 7 are formed in the PAE film 3 and the SiOC film 4.
Subsequently, an etching stopper film 8, a first insulating film 9
and a second insulating film 10 are sequentially deposited over the
Cu interconnects 7 and the SiOC film 4. The steps thus far are
carried out in the same way as the first embodiment.
[0122] Subsequently, sequentially formed over the second insulating
film 10 are a first-mask forming layer 31, a second-mask forming
layer 32, a third-mask forming layer 33 and a fourth-mask forming
layer 34, similarly to the first embodiment. The materials and
deposition methods of the respective mask forming layers are the
same as those in the first embodiment. In contrast, the thicknesses
of the layers in the third embodiment are different from those in
the first embodiment. Specifically, the thicknesses of the first-
to fourth-mask forming layers 31, 32, 33 and 34 are 70 nm, 70 nm,
50 nm and 50 nm, respectively. A resist mask 15 having a via hole
pattern is formed on the fourth-mask forming layer 34.
[0123] Referring next to FIG. 5B, the fourth-mask forming layer
(SiO.sub.2) 34, the third-mask forming layer (SiN) 33 and the
second-mask forming layer (SiO.sub.2) 32 are etched by dry etching
that employs the resist mask 15 (see FIG. 5A) as the etching mask.
Thus, a via hole pattern is formed in the fourth-mask forming layer
34, the third-mask forming layer 33 and the second-mask forming
layer 32. Subsequently, ashing treatment based on O.sub.2 plasma
and chemical treatment are implemented for example, to thereby
completely remove the resist mask 15 and residual fouling produced
in the etching treatment.
[0124] Referring next to 12C, a planarization layer 35 composed of
e.g. an organic material is formed on the fourth-mask forming layer
34 in a manner of filling the via hole pattern, and then a mask
transfer layer 36 composed of e.g. SiO.sub.2 is formed on the
planarization layer 35. Subsequently, a resist mask 14 having an
interconnect trench pattern is formed on the mask transfer layer
36.
[0125] Referring next to FIG. 5D, the mask transfer layer 36 and
the planarization layer 35 are formed by dry etching in which the
resist mask 14 (see FIG. 5C) is used as the etching mask. This
etching is carried out such that the planarization layer 35 remains
in the via hole pattern formed in the fourth-mask forming layer 34,
the third-mask forming layer 33 and the second-mask forming layer
32.
[0126] Referring next to FIG. 5E, the fourth-mask forming layer
(SiO.sub.2) 34 (see FIG. 5D) is etched by dry etching in which the
mask transfer layer 36 (see FIG. 5D) and the planarization layer 35
that have the interconnect trench pattern are used as the mask.
Thus, a fourth mask 34' having the interconnect trench pattern is
formed. This etching exposes the third-mask forming layer (SiN) 33
having the via hole pattern at the bottom of the interconnect
trench pattern of the fourth mask (SiO.sub.2) 34'. The mask
transfer layer 36 is removed in this etching.
[0127] Subsequently, as shown in FIG. 5F, ashing treatment based on
O.sub.2 plasma and chemical treatment are implemented for example,
to thereby completely remove the remaining planarization layer 35
(see FIG. 5E) and residual fouling produced in the etching
treatment. Through the above-described steps, the fourth mask 34'
having the interconnect trench pattern is formed on the third-mask
forming layer 33 having the via hole pattern.
[0128] Referring next to FIG. 5G, the third-mask forming layer
(SiN) 33 (see FIG. 5F) is etched by dry etching that employs the
fourth mask (SiO.sub.2) 34' having the interconnect trench pattern
as the etching mask. Thus, a third mask 33' having the interconnect
trench pattern is formed. Furthermore, in this etching, the via
hole pattern is extended downward with the third-mask forming layer
(SiN) 33 having the via hole pattern serving as the mask, so that
the second insulating film (PAE) 10 is exposed. Thus, the via hole
pattern is formed in the first-mask forming layer 31.
[0129] Subsequently, as shown in FIG. 5H, via holes 16 are opened
in the second insulating film (PAE) 10 by dry etching that employs
the second-mask forming layer 32 having the via hole pattern as the
etching mask, so that the surface of the first insulating film
(SiOC) 9 is exposed. In this etching, the etching selection ratio
of PAE to SiO.sub.2 is 100 or more. Therefore, this etching hardly
reduces the thicknesses of the fourth mask (SiO.sub.2) 34' and the
second-mask forming layer (SiO.sub.2) 32, which is exposed at the
bottom of the interconnect trench pattern of the third mask
33'.
[0130] Referring next to FIG. 5I, the second-mask forming layer 32
(see FIG. 5H) having the via hole pattern is etched by dry etching
in which the fourth mask 34' (see FIG. 5H) and the third mask 33'
having the interconnect trench pattern are used as the etching
mask. Thus, a second mask 32' having the interconnect trench
pattern is formed. In this etching, the fourth mask 34' is removed
in step with progress of etching of the second-mask forming layer
(SiO.sub.2) 32 since the fourth mask (SiO.sub.2) 34' and the
second-mask forming layer 32 are formed of the same material
(SiO.sub.2). Furthermore, this etching extends the via holes 16
downward partway across the first insulating film (SiOC) 9.
[0131] Referring next to FIG. 5J, the first-mask forming layer
(SiOC) 31 (see FIG. 5I) is etched by dry etching that employs the
third mask 33' having the interconnect trench pattern as the
etching mask. Thus, a first mask 31' having the interconnect trench
pattern is formed. Moreover, due to this etching, the via holes 16
are further extended downward with the first-mask forming layer
(SiOC) 31 and the second insulating film 10 having the via hole
pattern serving as the mask, so that the etching stopper film 8 is
exposed.
[0132] The subsequent steps are carried out in the same way as the
first embodiment. Specifically, referring next to FIG. 5K, the
etching stopper film 8 remaining under the bottoms of the via holes
16 and the third mask (SiN) 33' (see FIG. 5J) are etch-removed.
Subsequently, the second insulating film (PAE) 10 remaining under
the bottom of the interconnect trench pattern in the first mask
(SiOC) 31' is etched with use of the second mask (SiO.sub.2) 32' as
the etching mask. Thus, the interconnect trench pattern formed in
the first mask 31' is extended downward, which results in the
formation of interconnect trenches 17 in the second mask 32', the
first mask 31' and the second insulating film 10.
[0133] After the above-described steps, by posttreatment employing
chemicals and RF-sputtering treatment, etching fouling that remains
on sidewalls of the interconnect trenches 17 and the via holes 16
are removed, and modified Cu layers at the bottoms of the via holes
are converted to normal Cu layers.
[0134] Thereafter, as shown in FIG. 5L, a barrier metal film 18 is
deposited by sputtering in a manner of covering the inside walls of
the interconnect trenches 17 and the via holes 16. Subsequently, a
conductive film 22 composed of Cu is deposited on the barrier metal
film 18 by electrolytic plating or sputtering in a manner of
filling the interconnect trenches 17 and the via holes 16. Thus,
the interconnect trenches 17 and the via holes 16 are
simultaneously filled.
[0135] Referring next to FIG. 5M, by using CMP, extra part of the
conductive film 22 (see FIG. 5L) and the barrier metal film 18
unnecessary as the interconnect pattern is removed. In addition,
the whole second mask 32' and upper part of the first mask 31' are
also removed. Thus, vias 19 are formed in the via holes 16 while Cu
interconnects 20 are formed in the interconnect trenches 17. In
this step, the polishing time period of the CMP is adjusted so that
the thickness of the Cu interconnects 20 becomes 140 nm. Moreover,
an etching stopper film 21 composed of e.g. SiC is formed on the Cu
interconnects 20 and the first mask 31', similarly to the etching
stopper film 8 on the lower Cu interconnects 7. Accordingly, a
multilevel interconnect structure based on a dual damascene
structure can be achieved.
[0136] According to the above-described manufacturing method of a
semiconductor device, the first mask 31' is left on the second
insulating film 10, and serves as a third insulating film that
defines the interconnect trenches in association with the second
insulating film 10. Since the first insulating film 9, the second
insulating film 10 and the first mask 31' are each formed of a
low-k material, the third embodiment can offer the same advantages
as those of the first embodiment.
[0137] Moreover, since the whole second mask 32' and upper part of
the first mask 31' in addition to extra part of the conductive film
22 unnecessary as the interconnect pattern are removed by CMP, the
second mask 32' having a high dielectric constant can surely be
removed. This ensured removal of the second mask 32' facilitates
control of the dielectric constant compared with the case where
polishing residues of the second mask 32' partially remain.
[0138] In the above-described first and second embodiments, the
vias 19 and the Cu interconnects (upper interconnects) 20 are
aligned with the Cu interconnects (lower interconnects) 7, and
these two alignment steps induce misalignment between the vias 19
and the Cu interconnects 20. In contrast, in the third embodiment,
the vias 19 are aligned with the Cu interconnects 7, and then the
Cu interconnects 20 are aligned with the vias 19. Therefore, a
margin for short-circuit between vias and interconnects at
different potentials can be enlarged.
[0139] Note that features of the modifications of the first
embodiment and features of the second embodiment are available also
in the third embodiment.
(First Working Example)
[0140] Semiconductor devices were manufactured by the same method
as that of the second embodiment, with the thickness of the second
etching stopper film (SR--SiO.sub.2) 8b being changed on each
device basis from 5 nm to 20 nm by an increment of 5 nm. The
interconnect capacitances of the manufactured devices were
measured. In addition, a semiconductor device having no second
etching stopper film 8b (i.e., the thickness thereof was 0 nm) was
also manufactured by the same method as that of the first
embodiment, and the interconnect capacitance thereof was measured.
FIG. 6 is a graph showing the measurement results of the
interconnect capacitances of these semiconductor devices. Note that
the interconnect capacitances are indicated as the ratio with
respect to the interconnect capacitance of the semiconductor device
in FIG. 7H. That is, the interconnect capacitance of the device in
FIG. 7H is defined as 1.
[0141] This graph shows that, when the thickness of the second
etching stopper film 8b is 20 nm or smaller, an interconnect
capacitance smaller by 3 to 7% than that of the semiconductor
device with the conventional structure is obtained.
[0142] It should be understood by those skilled in the art that
various modifications, combinations, sub-combinations and
alterations may occur depending on design requirements and other
factors insofar as they are within the scope of the appended claims
or the equivalents thereof.
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